You might have a bios support issue with the motherboard. Check the cpu support list on the website for the motherboard maker. They usually say in a newer version of a bios is needed to make a cpu work. Also try doing a CMOS clear as the system could be set to boot video from something other than PCI.

Oh you could also have a video card voltage issue. Newer motherboards only work with 3.3 volt PCI devices.